1. Field of the Invention
The present invention relates to plasma processing apparatuses. In particular, the present invention relates to a plasma processing apparatus such as etching, film deposition and ashing apparatuses used for manufacturing semiconductor devices or liquid crystal display devices, for example.
2. Description of the Background Art
A plasma process by means of microwave now captures attention as that is applicable to a low-temperature plasma process for a semiconductor device or TFT (thin film transistor) liquid crystal display device for example. What is important here is that such a plasma process is uniformly carried out for a substrate. In addition, under a low gas-pressure condition of 0.133 Pa or lower, discharge tends to be difficult to start. This tendency is pronounced particularly when a gas with a high ionization voltage is used.
These problems are addressed as disclosed in Japanese Patent Laying-Open Nos. 5-36641 and 2000-91097 showing methods for achieving uniform plasma and in Japanese Patent Laying-Open No. 9-232099 showing a method for improving a plasma generation property.
The method disclosed in Japanese Patent Laying-Open No. 5-36641 is described below.
FIG. 13 is a schematic cross section showing a structure of a plasma processing apparatus disclosed in Japanese Patent Laying-Open No. 5-36641. Referring to FIG. 13, a chamber body 101 and a dielectric plate 103 are sealed by an O-ring (not shown) in order to isolate a process chamber 100 from the atmosphere. The air inside process chamber 100 is discharged by an exhaust device (not shown) until a predetermined vacuum pressure is attained. Then, a process gas is supplied from a gas inlet 109 into process chamber 100. A microwave generated by a microwave generator (not shown) is thereafter supplied through a waveguide 106 into a microwave stirrer chamber 102. An impeller 108 is rotated by a drive motor 107 to stir and disperse the microwave within microwave stirrer chamber 102. The stirred microwave is passed through dielectric plate 103 into process chamber 100. The process gas is thus excited to generate plasma. This plasma is used to plasma-process a substrate 105 held on a substrate holder 104.
Japanese Patent Laying-Open No. 2000-91097 discloses a technique as discussed below.
FIGS. 14 and 15 are schematic cross sectional and plan views respectively of a structure of a plasma processing apparatus disclosed in Japanese Patent Laying-Open No. 2000-91097. Referring to FIGS. 14 and 15, the air inside a process chamber 100 is discharged by an exhaust device (not shown) until a predetermined vacuum pressure is attained, and a process gas is thereafter supplied from a gas inlet 109. A microwave generated by a microwave generator 122 is guided though a waveguide 114 and a dielectric line 115 to the top of process chamber 100. The microwave radiated from dielectric line 115 is passed though a microwave dispersion plate 120 formed of three plates stacked on each other as well as a microwave entrance window 116 into process chamber 100 for generating plasma from the process gas. Then, a substrate 105 held on a substrate holder 104 is plasma-processed.
Microwave dispersion plate 120 is constituted of two dielectric plates 117 and 119 and a plurality of thin aluminum sheets 118 arranged at certain intervals between the two dielectric plates, and this microwave dispersion plate 120 serves to disperse the microwave.
Japanese Patent Laying-Open No. 9-232099 discloses a technique as described below.
FIG. 16 is a schematic cross section showing a structure of a plasma processing apparatus disclosed in Japanese Patent Laying-Open No. 9-232099. Referring to FIG. 16, the air inside a process chamber 100 is discharged by an exhaust device (not shown) until a predetermined vacuum pressure is attained and then a process gas is supplied from a gas inlet 109. A microwave generated by a microwave generator 123 is guided through a waveguide 124 via a matching unit 125 to the top of a microwave entrance window 126. Then, the microwave is passed through microwave entrance window 126 made of dielectric to be radiated into process chamber 100. On one side of microwave entrance window 126 that faces process chamber 100, a depression 126a is provided. The process gas supplied from gas inlet 109 into process chamber 100 is excited by the microwave radiated from microwave entrance window 126 to generate plasma. Then, a substrate 105 on a substrate holder 104 is plasma-processed.
Depression 126a which deforms microwave entrance window 126 can cause plasma concentration so that the plasma generation property can be improved.
However, the plasma process is difficult to make uniform by the methods described above when the methods are used for a TFT liquid crystal display device with a substrate of a size ranging from 500×500 mm to 1 m×1 m. There are thus problems in respective methods described above.
In the apparatus of Japanese Patent Laying-Open No. 5-36641, the microwave is stirred by impeller 108 and then supplied into process chamber 100. This is effective to some degree for circular substrate 105. However, the microwave uniformity is unsatisfactory for a rectangular substrate. Moreover, although impeller 108 is advantageously used to apply the microwave almost uniformly to a substrate of a small area, such a microwave is difficult to apply to a rectangular substrate of a large area. In other words, it is considerably difficult to design stirrer chamber 102 and impeller 108 that are to be used for uniformly supplying the microwave into process chamber 100.
A plurality of stirrer chambers 102 and impellers 108 might be provided. However, problems arise in terms of control of impellers 108 and maintenance.
In the apparatus of Japanese Patent Laying-Open No. 2000-91097, the microwave is dispersed by microwave dispersion plate 120. The performance of microwave dispersion plate 120 is determined by the thickness and arrangement of aluminum sheets 118 between two dielectric plates 117 and 119. However, optimization of the thickness and arrangement of aluminum sheets 118 for the purpose of dispersing and uniformly supplying the microwave is difficult to accomplish. In addition, it is hard to produce microwave dispersion plate 120 which is applicable to large-area substrates.
This plasma processing apparatus uses dielectric line 115 from which the microwave is supplied. Dielectric line 115 guides the microwave generated by generator 122 to the top of process chamber 100 so as to radiate the microwave into chamber 100 from a radiation plate which is larger in size than substrate 105. Dielectric line 115 is made of dielectric such as Teflon (trade name) that includes a tapered portion T with its width increasing from the one on one end corresponding to the width of the output opening of generator 122 to the width on the other end corresponding to the width of the microwave radiation portion. In order to transmit the microwave without change of the propagation mode, tapered portion T of dielectric line 115 should gradually be tapered. Then, in order to adapt dielectric line 115 to a large-area substrate, tapered portion T is made considerably long. Consequently, when the apparatus is used for a large substrate 105, the apparatus increases in size to occupy a large installation area.
In the apparatus of Japanese Patent Laying-Open No. 9-232099, depression 126a is provided as shown in FIG. 16 on the side of microwave entrance window 126 that faces process chamber 100 in order to improve the plasma generation property. Depression 126a is utilized to cause, in process chamber 100, a high field-intensity region to be generated near depression 126a in order to facilitate plasma generation.
The presence of the high field-intensity region in the apparatus certainly improves the plasma generation property. However, the region where the field intensity is high remains near depression 126a even after the plasma is generated. Accordingly, the plasma density in that region is high which makes it impossible to uniformly distribute the plasma and thus to uniformly perform a plasma process for substrate 105.